HP 212M, 224M manual How STP Operates, Example of Active and Backup Paths Between Two Nodes

Configuring the Switch

Spanning Tree Protocol (STP)

4.If the remaining STP parameter settings are correct for your network, go to step 7.

5.Use [Tab] or the arrow keys to select the next parameter you want to change, then type in the new value. (If you need information on STP parameters, press [Enter] to select the Actions line, then press [H] to get help.)

6.Repeat step 5 for each additional parameter you want to change.

7.When you are finished editing parameters, press [Enter], then press [S] (for Save) and return to the Switch Configuration menu.

How STP Operates

When STP is enabled, the switch automatically senses port identity and type, and automatically defines port cost and priority for each type. The switch console allows you to adjust the Cost and Priority for each port, as well as the global STP parameter values for the switch.

In the event of a topology change such as a switch, bridge, or data link failure in the network, STP develops a new spanning tree that may result in changing some ports from the blocking state to the forwarding state.

If an active path fails, STP automatically activates (unblocks) an available backup to serve as the new active path for as long as the original active path is down. As shown in the following illustration, the active path between nodes A and B uses links 1 and 3 which have a lower total path cost than the path using links 4, 2, and 3. If link 1 happens to go down, path 4→2→3 becomes the active path.

•Active path from node A to node B: 1→3

•Backup (redundant) path from node A to node B: 4→2→3

Configuring the Switch

1

path cost: 100

switch B

node

A

switch A

2

path cost: 100 switch C

4

path cost: 200

3

path cost: 100

switch D

node

B

Figure 6-16. Example of Active and Backup Paths Between Two Nodes

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